1. Field of the Invention
The present invention relates to an electrodynamic ultrasonic transducer including a housing to be placed against a workpiece surface to be tested and a magnet system arranged in the vicinity of the workpiece surface to be tested. The transducer further includes a transducer coil system arranged between the magnet system and the workpiece surface to be tested.
2. Description of the Related Art
Electrodynamic ultrasonic transducers are used in non-destructive ultrasonic material testing. In operation of electrodynamic ultrasonic transducers, the ultrasound is produced in the workpiece to be tested by eddy current induction through a magnetic field and a transducer coil which essentially acts as an antenna. Accordingly, the ultrasound is produced only in the workpiece surface to be tested itself and not already in the ultrasonic transducer, as is the case in piezoelectric ultrasound production. For this reason, the use of ultrasonic coupling means between transducer and workpiece surface is unnecessary in electrodynamic ultrasound production.
An electrodynamic ultrasonic transducer of the above-described type is known from DE 40 16 740 C1. This electrodynamic ultrasonic transducer is now used in automated ultrasonic testing, as well as in ultrasonic testing conducted manually. This known electrodynamic ultrasonic transducer is of very compact construction, so that the device is suitable as a hand-held test device and can be mounted individually in a large testing plant which has a plurality of such testing devices.
In the known electrodynamic ultrasonic transducer, the entire magnet arrangement is fixed because of the geometry of the transducer. The sound incidence direction of the ultrasonic waves generally depends on the geometric configuration of the magnets and, more significantly, on the geometric configuration of the coils. Since, in addition to testing a wall thickness, volumetric testing and testing for internal defects and surface defects are important, the magnet arrangement and coil geometry must be adapted to each other. Also, wave modes of different polarization which are adjusted to the desired testing task require an adaptation or change of the coil geometry and possibly of the magnet geometry. While the adaptation of the ultrasonic transducer to different coil geometries is possible in this known ultrasonic transducer, the adaptation is difficult and complicated.
When the ultrasonic transducer is used mounted individually in a large testing plant as mentioned above, depending on the type of testing plant there are large distances between the ultrasonic transducer and a central electronic control unit. However, the use of an electronic unit at the test site on the ultrasonic transducer itself is not possible in this known ultrasonic transducer under difficult conditions of operation, for example, at higher temperatures. The construction of the known electrodynamic ultrasonic transducer requires that the temperature of operation, i.e., essentially the temperature of the workpiece to be tested, is not greater than about 80.degree. C. The known ultrasonic transducer makes possible the electrodynamic production of ultrasound in a very advantageous compact manner, however, the transducer is not suitable for a simple and quick rearrangement of the magnet geometry and the coil geometry and cannot be easily used over large distances between the transducer and the electronic control unit and at high temperatures.